Effects of polymeric charge variations on the proton‐metal ion equilibria of humic materials

Abstract

Except for specific molecular weights, humic materials have many of the chemical and physical characteristics of enzymes. Thus modified equations from the biochemical literature can provide a theoretical description of proton-metal ion interactions on humic substances. For a given ionizable group type, the members of the group are chemically identical within experimental error, and the observed variations in dissociation of humic acid and bonding strength of metal ion as a function of pH are quantitatively related to the electrostatic interaction between the cationic species and the negatively charged humic polyion. This approach allows experimental determination of intrinsic constants for dissociation of acid and formation of metal ion, i.e. equilibrium constants which are independent of all electrostatic effects. The intrinsic constants obtained for a few humic materials are compared to those of possible monomeric units. In addition, the intrinsic constants have been coupled with other experimental parameters to predict the concentration of metal ion bound to humic materials as a function of pH.

An assessment of mercury-species-dependent binding with natural organic carbon

“…As with all polyelectrolytic phenomena, this property is sensitive both to net charge and ionic strength. Previous approaches to quantifying this effect with organic matter include relatively simple exponential electrostatic corrections (Wilson and Kinney, 1977;Tipping and Hurley, 1992) and a Donnan potential-type term (e.g. Marinsky and Ephraim, 1986).…”

Etude par D.PA.S.V. de l'aptitude de la matdere organique colloidale a fixer et a transporter les metaux: Exemples de bassins versants en zone tropicale

“…Les interactions alors mises en jeu ne sont pas uniquement regies par les lois habituelles de la thermodynamique des solutions. Des forces electrostatiques (Coulomb, Van Der Waals) interviennent (19,20). A la surface d'un colloi'de ces interactions doivent egalement etre prises en compte.…”

Competitive Adsorption of Heavy Metals in Humic Substances by a Simple Ligand Model

“…free energy arising from the surface charge on the molecule. Several researchers have applied electrostatic models to Cu, Al, Mn, Zn, and Cd adsorption by humic substances and synthetic polycarboxylates (Wilson and Kinney, 1977;Young et al, 1982;Young and Bache, 1985;Backes and Tipping, 1987). This simple approach has been criticized on various grounds, however.…”